In Serbia, reformist candidate Boris Tadic is ahead of his nationalist rival in opinion polls at the close of a campaign for Sunday's crucial presidential run-off election. However, political analysts caution the outcome of the election very much hinges on voter turnout.

Backed by European Union leaders and a score of reformist politicians, Serbia's pro-Western presidential candidate, Boris Tadic, hopes voters will turn out in large numbers in Sunday's runoff presidential ballot.

A low turnout, according to observers, would favor the more disciplined supporters of the nationalist candidate, Tomislav Nikolic, whose Serbian Radical Party is the biggest political faction in parliament. Mr. Nikolic got more votes in the first round of balloting than his moderate challenger.

Earlier this week, millions of Serbian television viewers got a closer look at the candidates during a debate on issues ranging from the future of Kosovo to cooperation with the United Nations War Crimes Tribunal and membership in the European Union.

Mr. Nikolic declared, if elected, he would never allow Kosovo, which he calls the cradle of Serbia, to break away. Although Kosovo is officially part of Serbia, it has been under United Nations administration since 1999 when NATO forced Serb troops to withdraw.

He also indicated that, as president, he would oppose independence for Montenegro, a small coastal republic that now forms a loose union with Serbia, and would not be in any rush to join the European Union.

He also said he would never force any Serb to surrender to the U.N. War Crimes tribunal to answer charges stemming from the Balkan wars of the 1990s in which an estimated quarter of a million people died.

By contrast, the pro-Western Boris Tadic said in debate he consider Serbia's cooperation with the United Nations and the European Union as the only way to end Serbia's isolation.

"Serbia needs a relationship with the outside world, as it cannot exist on its own," he said. He says it is especially important to work with "rich and powerful partners," including the EU, the United States and Serbia's neighbors.

Analysts like Dragana Solomon of the independent Institute for War and Peace Reporting warn that a voter turnout of 40 percent or less would likely spell defeat for Mr. Tadic.

"Simply, Serbian voters are tired of voting," Ms. Solomon said. "You know people say to me, 'Oh, it doesn't matter, my life will not change dramatically if I went to vote, so I am staying at home.' All the analysts here [agree] that there is a clear mathematics. If more than 2.5 million voters will come out, Tadic will win. If less than 2.5 half-million come out, Nikolic will win. So the less they come out [the more] the radicals will win."

She says a victory by Mr. Nikolic may well heighten ethnic tensions in Serbia and return the country into isolation.

"He is speaking to the core of his electorate, which is comprised of nationalists who still think that there is a possibility of Serbia's army and police to come back to Kosovo and take it over," she explained. "If Nikolic wins the election, Serbia will be isolated. Europe will just leave Serbia alone for a while, and there will be a danger of reforms stalling. At the moment the process of cooperation with The Hague is not going very well, but is seems to me that if Nikolic gets into power, it will even go from bad to worse."

However, even with Mr. Tadic as president, analysts say the polarized Serbia is in for a period of political volatility, as the elected leaders try to balance the conflicting interests of political parties that back them.